We are concerned with enzymological aspects of DNA replication in bacteria infected with T-even bacteriophages. This work includes (1) studies on DNA-defective mutants of phage T4, with the aim of identifying the mutationally altered function leading to defective DNA replication; (2) studies on nucleotide metabolism in phage-infected bacteria, directed both toward an understanding of the intracellular regulation of phage-induced enzymes and resolution of the question of whether deoxynucleoside triphosphates are the intracellular precursors in DNA replication and also an understanding of intracellular compartmentation of DNA precursors; (3) molecular characterization of enzymes of DNA precursor metabolism; (4) analysis of T4 DNA replication in vivo; and (5) investigation of the process of restriction of non-glucosylated DNA by E. coli and the relation of this process to phage DNA replication.